The amount of the mineral fraction varies strongly, depending on the collection system (size of bins), on the collection area (rural or urban) and on the soil conditions in the region (e.g. sandy soil). Important is how much garden waste is collected for the anaerobic digestion and how much sand or other mineral fraction is adhered to the garden waste. To calculate a sand separator in the planning phase of a new plant, or for to retrofit one at an existing plant, the amount and the composition of the mineral fraction in the biowaste is very important.
At the moment there is no standard for the analysis of the mineral content in biowaste. The relevant literature and standards only describe the analysis of sand and mineral fraction in soil. The Institute of Waste Technology and Environmental Control (IfAU), at the University of Applied Sciences Braunschweig/Wolfenbüttel, compared three methods to determine the mineral content in biowaste Graul, 1999; Pelz, 1998). The two methods which were developed by IfAU and the third which is a modified one according to VDLUFA has been compared and evaluated concerning its range of use.